Common Manure Handling Systems
Swine manure was historically handled as a solid, either deposited directly by grazing animals, or collected in bedding placed on solid shelter floors to absorb the urine. Pastured animals spread the manure over the land as they grazed. Manure deposited on solid floors is typically stored where it falls, with more bedding added as needed to maintain a dry floor. Liquid drains away from the manure dropped on an outside lot and must be collected in a storage, leaving the solid manure behind. The manure composts in place somewhat and is removed every few months. Fertilizer value is recovered by spreading on cropland to complete the nutrient cycle. Solid manure is normally surface applied, but in some cases may be incorporated into the soil with a farm tillage operation shortly after spreading. Composting is another option for solid manure management.
Manure is typically scraped from outside lots every week or two and stacked until it can be hauled to cropland. It is important to keep an outside lot relatively free of manure to control odor and so that rainfall runoff stays mostly free of manure. This facilitates storage of relatively clean runoff for irrigation onto cropland. It is even possible to divert runoff from small operations directly to pasture or to a vegetated filter strip where it can infiltrate. It must be prevented from entering waterways. Clean upslope water and roof water should be diverted away from the open lot to minimize the amount of wastewater that must be handled as a manure.
Most swine manure is handled as a liquid. Manure typically falls through a slotted floor (with the size of slot depending on the size and age of animal) into either a gutter or a concrete storage pit. Storage pits provides from 3-12 months storage of the manure. This pit may either be located directly under the slotted floor and may be from 4' to 10' deep. In some operations, the manure falls into a shallow pit or gutter which is periodically pumped, flushed or drained to a large outside storage. The outside storage may either be constructed in the earth or a commercial steel or concrete storage purchased and erected onsite . Storage size is dictated by regulatory agencies in most states and are usually sized large enough to hold at least six month’s accumulation in Midwestern states. This avoids the need to apply manure during the crop growing season and when weather conditions are unsuitable – such as on frozen ground or when the soil is wet enough that heavy application vehicles could compact and damage the soil for crop production.
Liquid manure from storage is normally agitated thoroughly to make the manure nutrient content between loads more uniform and hauled to the field for application in large tanker wagons or trucks. Liquid manure is either applied to the soil surface or is incorporated during or shortly after application to control loss of volatile ammonia and release of odors. Incorporation is very effective at controlling runoff of manure nutrients and reducing odor from land application if done during or within a few hours after application. One method is a soil injector, where liquid manure is “injected” directly into the soil to a depth of 6 to 9” as the tanker passes over the field. This immediate contact between the manure and soil is highly effective at controlling odor.
In remote areas, liquid manure may be pumped to the land application site
and then irrigated onto cropland. Spray irrigating liquid manure is
a very efficient method of land application, in terms of speed and labor,
but odor emissions can be significant; therefore, it is not feasible to
use this method in populated areas.
Lagoons are different from liquid manure storage because they are operated
to encourage anaerobic digestion of organic material while it is being stored.
This reduces odor when the treated manure is land applied. A properly designed
and operated treatment lagoon is much larger and more expensive than a liquid
manure storage with the same storage time, and the organic solids are much
less concentrated in the liquid.
In the Midwest, an equal part of relatively clean dilution water must be added for each part manure. Furthermore, manure must be added slowly and uniformly to the lagoon, to avoid an upset (and subsequent release of odors) to the biological treatment system. One common method of doing this is to utilize shallow pits or gutters under slotted floors and drain or flush manure to the lagoon on a frequent basis, usually every three days to three weeks. This is done by simply pulling a plug in the bottom of the pit, called gravity drain, use of a scraper system running in the underfloor gutter, through a process called a "hairpen" gutter or by recirculating a volume of relatively clean effluent from the lagoon to flush manure out of the building and into the lagoon. Recirculation involves either a flushing action that takes place several times a day or a "pit recharge" system that works basically like a toilet that is flushed every few days.
A portion of the lagoon contents or "minimum design volume" must be left in the lagoon after its contents are pumped to the land to provide a large number of microbial organisms to treat the new manure entering the system. In spite of proper operation, there is an “over turning” of the lagoon contents that occurs in the fall of the year for a couple of weeks, as ambient temperature drops and cools the top layer of liquid in the lagoon. As its density increases, it “overturns” or drops to the bottom of the lagoon, forcing the bottom layer, containing partially digested manure solids, to the top. This phenomenon results in higher odor levels for a week or two around the lagoon. Multiple Lagoons in series normally emit fewer odors than single cell lagoons.
Lagoon contents are normally applied to cropland by spray irrigation systems. If the lagoon is properly designed and operated, spray irrigation should not release much odor because most of the organic solids should have been biologically degraded. In a well-operated lagoon, typical effluent should have only about 20% as much nitrogen (N) and about 30% to 40% as much phosphorous (P) and potassium (K) as the raw manure, because of treatment and sedimentation of solids to the bottom of the lagoon. Note that the P and K "lost" actually accumulate in the sludge and must be utilized properly when removed. These solids, or sludge, must be removed every few years and the operation should plan to handle them as a part of their nutrient management plan. Because this material is more concentrated, it may be practical to haul the sludge off site to more distant cropland that can better utilize the nutrients contained in the sludge. Because of the nuisance potential of this partially stabilized material, it should be incorporated as a liquid manure if possible.